SA56004X Datasheet, PDF (17/36 Pages) NXP Semiconductors – 1 Degrees Celcious accurate, SMBus-compatible, 8-pin, remote/local digital temperature sensor with over temperature alarms

NXP Semiconductors
SA56004X
Digital temperature sensor with overtemperature alarms
Event F: Three consecutive measurements have been made with the remote
temperature below the RCS − TH threshold; the T_CRIT output is de-activated (goes
HIGH).
Event G: The remote temp falls below the Remote LOW setpoint.
Event H: Three consecutive measurements are made with the temp below the Remote
LOW setpoint; ALERT output is activated (goes LOW).
Event I: The ALERT output is de-activated (goes HIGH) after a above_low_limit
temperature measurement is completed.
7.9.4 Remote diode selection
To measure the remote temperature or the temperature of an externally attached diode,
the device automatically forces two successive currents of about 160 µA and 10 µA at D+
pin. It measures the voltage (V_BE) between D+ and D−, detects the difference between the
two V_BE voltages or the ∆V_BE and then converts the ∆V_BE into a temperature data using
the basic PTAT voltage formula as shown in Equation 1. The device typically takes about
38 ms to perform a measurement during each conversion period or cycle, which is
selectable by programming the conversion rate register.
∆V _BE
=
n
×
k_--q--T_--
×
ln


ll_---21_{-}
(1)
Where:
n = diode ideality factor
k = Boltzmann’s constant
T = absolute temperature (°K) = 273 °C + T (°C)
q = electron charge
ln = natural logarithm
l2, l1 = two source currents
Because the device does not directly convert the sensed V_BE as in the old method of
temperature measurement systems, the V_BE calibration is not required. Furthermore, the
device remote temperature error is adjusted at the manufacturer to meet the specifications
with the use of the reference diode-connected transistors such as the 2N3904/2N3906.
The diode type to be used in customer applications must have the characteristics as close
to the 2N3904/2N3906 as possible in order to obtain optimal results. Finally, to prevent the
effects of system noise on the measured V_BE signals, an external capacitor of about
2200 pF connected between the D+ and D− pins as well as the grounded-shield cable for
the diode connection wires are recommended.
7.9.5 Diode fault detection
The SA56004X is designed with circuitry to detect the fault conditions of the remote diode.
When the D+ pin is shorted to V_DD or floating, the Remote Temperature High Byte (RTHB)
register is loaded with +127 °C, the Remote Temperature Low Byte (RTLB) register is
loaded with 0 °C, and the OPEN bit (bit 2 of the Status register) is set. Under the above
conditions of D+ shorted to V_DD or floating, if the Remote T_CRIT setpoint is set less than
+127 °C, and T_CRIT Mask are disabled, then, the T_CRIT output pins will be pulled
SA56004X_5
Product data sheet
Rev. 05 — 22 May 2008
© NXP B.V. 2008. All rights reserved.
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